The present invention on in general relates to a machine tool such as turning machine or a machining center. More specifically, this invention relates to a machine tool in which a faulty tool can be identified.
In a machine tool, sometimes a tool (e.g., a twist drill) gets broken or damaged, or chips twine around a drill while the matching is repeated many times. Since appropriate working (matching) cannot be continued in this situation, the drill has to be replaced, or chips twining around the drill have to be removed. Whether or not the drill is broken/damaged or whether or not chips twine around the drill can be, for example, confirmed by a human eye. However, in the case of unmanned operation, it is necessary to determine without human help whether or not the drill is broken/damaged or whether or not chips twine around the drill in a machine tool.
For example, a machine tool is known in which a value of the current flowing in a motor which rotates the drill is monitored, and it is detected based on this value whether the drill is faulty. When the drill is normal, it properly cuts the job. In this case, there is a load on the motor, and therefore the current value is large. When the drill is faulty, it does not properly cut the job. In this case, there is less load on the motor, and therefore the current value is small. This numerically controlled (NC) machine tool determines whether or not the drill is faulty based on the difference between the current value when the tool is normal and the current value when the tool is faulty.
In another conventional NC machine tool, a touch sensor is provided which is in contact with a drill. This sensor determines whether or not the drill is faulty. In still another conventional NC machine tool, an image of the drill is photographed by a CCD camera. This image is used to determine whether or not chips twine around the drill.
Thus, in the conventional NC machine tool which detects the faulty tool based on the current value, whether or not the tool is faulty is determined based on the difference between the current value of the normal time and the current value of the breakage/damage time. However, if the cutting load is very small, as in a case in which a tool diameter is 2 mm or smaller (particularly 0.2 mm diameter or less), the difference between the current values when the tool is normal and when the tool is faulty is very small, and it is very difficult to determine whether the tool is normal or faulty.
In the conventional NC machine tool in which the faulty tool is detected using a touch sensor, the touch sensor is in contact with a tool. However, if the strength of the tool is low, as in a case in which the tool diameter is 2 mm or smaller (particularly 0.2 mm diameter or less), the tool gets broken. The tool may be prevented from being broken/damaged by making the travel speed of the touch sensor extremely slow so as to place the sensor in contact with the tool with an extremely minute force. However, the time for determination a tool is broken/damaged is increased, thereby causing a disadvantage that the productivity is markedly reduced
With the conventional NC machine tool in which a drill is photographed by a CCD camera, the volume of the CCD camera is large and the camera is expensive. Therefore, there is a problem that the NC machine tool becomes large sized, and its cost increases.
It is one object of this invention to provide a machine tool in which even when the cutting load is minute and/or the strength of a tool is low, it is possible to automatically determine whether or not the tool is faulty. It is another object of this invention to provide a machine tool in which the machine tool can be miniaturized and thereby cost can be reduced.
The machine tool according to one aspect of the present invention comprises a photographing unit which photographs an image of the tool, and a determination unit which determines whether or not the tool is faulty based on the images obtained by the photographing unit. This, a faulty tool is detected using the images and there is nothing that comes in contact with the tool.
The photographing unit comprises an artificial retina chip. The artificial retina chip is small and inexpensive. Accordingly, the machine tool can be miniaturized, and the cost can be reduced.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.